1. Field of the Invention
This invention relates to transmission shafts and is particularly concerned with shafts for transmitting rotary motion.
2. Description of the Prior Art
It is known to provide, in such shafts, a circumferential recess in an external surface to purposely provide a weak spot which will attract a failure in the event of an overload of the shaft. Such a recess is known in the art as a shear neck.
Shear necks are used to protect valuable components from damage in the event of failure in a transmission system and are used, for example, in the transmission shafts in an accessory drive gearbox in a helicopter for driving accessories such as hydraulic pumps, generators etc. Thus a failure in one of the driven accessories will result in a failure at the shear neck in its particular drive shaft only and will not result directly in damage to other components of the system.
One of the problems in the use of existing shear necked transmission shafts is that debris from a failure is likely to contaminate the associated gearbox which may at best necessitate flushing the lubrication system and at worst damage other major gearbox components and necessitate a complete strip and clean operation.